The present invention relates to media for recording, storing and reading magnetic data, and more particularly to the use of radiant energy beams to control topographies of such magnetic media.
Magnetic disks employ thin films of magnetizable material for storing data in magnetic form. Typically magnetic disks are mounted to rotate, each of with magnetic data transducing heads positioned in close proximity to one of the magnetic disk recording surfaces. Each head is moved generally radially with respect to its associated disk as the disk is rotated. In drives that employ rigid magnetic disks, the disks are rotated at high speeds during reading and recording operations. The speed of rotation is sufficient to create an air cushion or bearing that supports each transducing head at a controlled distance from its associated recording surface, to maintain a consistent head "flying" height. The transducing heads contact their associated disks whenever the disks are stationary, accelerating from a stop, or decelerating just before coming to a complete stop.
Designers of magnetic disks continually strive to increase the density at which the magnetic data can be stored. One approach to increasing storage densities is to reduce the transducing head flying height. A smooth, specular recording surface, and a similar opposing surface of the transducing head, permit closer proximity of the head and recording surface. In addition to allowing greater data density, smooth surfaces result in more consistent and predictable behavior of the air bearing and head during operation.
At the same time, excessive smoothness can lead to friction and stiction problems when the transducing head contacts the disk. One solution, disclosed in U.S. Pat. No. 5,108,781 (Ranjan et al), involves selectively texturizing a predetermined portion of the disk surface, sometimes designated as the landing or contact zone. Then, the transducing head is positionally controlled so that whenever the disk decelerates toward a stop, the head engages the disk at the landing zone rather than at the relatively smoother recording surface. This patent further discloses the use of laser energy to control the landing zone texture. More particularly, a neodymium:yttrium aluminum garnet (Nd:YAG) laser generates a pulsed laser beam focused upon the upper surface of an aluminum nickel-phosphorous substrate. The laser forms a series of laser marks or spots, each including a central depression surrounded by an annular, raised rim.
While this approach remains satisfactory for most applications, there are certain particularly demanding circumstances for which the depressions and their surrounding rims result in excessive surface roughness, or lack sufficient uniformity. These applications involve further reductions in transducing head flying heights, for example to as low as a single microinch (25.4 nm). The lower flying heights also place severe demands upon the relatively smooth data recording surfaces of the magnetic disks. More particularly, the recording surfaces must be polished extremely smooth to avoid sharp peaks and other acicular features that might contact a low flying transducing head.
It is well known to polish disks mechanically, i.e. employing a saturated cloth, paper, or pad coated or flooded with cerium oxide, silicon carbide or another suitable grit. To achieve roughness levels of 0.1 microinch (2.54 nm) or less, the abrading process usually involves several stages of increasingly fine grit. Alternatively, mechanical polishing can involve a time consuming single stage, using a very fine grit material. In either event, a substantial amount of stock must be removed, considerably increasing media production costs and potentially degrading media quality due to an unwanted curvature near the edges. The residual scratches formed by mechanical polishing can cause defects in the subsequently applied magnetic recording film, due to replication of surface topography. These defects are a source of noise. The residual scratches also reduce the uniformity of a protective carbon film applied over the magnetic recording layer, which diminishes resistance to corrosion.
Therefore, it is an object of the present invention to provide a magnetic data recording medium in which the texture of a dedicated transducing head contact zone is more uniform and more precisely controlled.
Another object is to provide a process for directing a coherent energy beam onto an exposed surface of a magnetic recording medium, controlling the beam to control the height and structural features of nodules and other discontinuities.
A further object is to provide a process for selectively directing laser energy onto a data recording surface of a magnetic medium substrate after a surface of the substrate has been mechanically polished, to remove residual scratches without undesirably altering the character of the treated substrate.
Yet another object is to provide a magnetic data recording medium with a data recording surface that is smooth, essentially free of residual scratches and other acicular features, and more resistant to corrosion.